In a conventional mobile communication system, in an uplink from a mobile station UE to a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel, in consideration of radio resources of the radio base station Node B, an interference volume in an uplink, transmission power of the mobile station UE, transmission processing performance of the mobile station UE, a transmission rate required for an upper application, and the like, and to notify the determined transmission rate of the dedicated channel by a message in a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 10, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of channel (for example, per approximately 1 through 100 ms), due to processing load, processing delay, or the like.
In addition, in the conventional mobile communication system, there has also been a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the channel can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the channel is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 11(a), the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 11(b), or, as shown in FIG. 11(c), by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIG. 11.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
With reference to FIG. 12, descriptions will be given for a transmission power control in the enhanced uplink. To simplify the description, parts unnecessary for the description, such as an RF section and an antenna, are omitted in the example of FIG. 12.
Firstly, “inner-loop transmission power control” in the enhanced uplink will be described.
In step S101, a transmitter of a mobile station UE transmits data to a radio base station Node B via an uplink.
Here, the transmitter of the mobile station UE periodically transmits a dedicated physical control channel (DPCCH) to which layer 1 control information such as a pilot and a TPC command are mapped. Further, in accordance with presence or absence of data, presence or absence of a transmission allocation, or the like, the transmitter of the mobile station UE transmits either a dedicated physical data channel (DPDCH) or an enhanced dedicated physical data channel (E-DPDCH), to which user date or control information of layer 2 or higher are mapped.
In step S102, an SIR calculating section of a radio base station Node B calculates a signal-to-interference ratio (a reception SIR) of the received DPCCH, and compares a set target SIR with the calculated reception SIR.
In step S103, when the comparison result shows “received SIR>target SIR”, the SIR calculator notifies the transmitter to transmit a “Down” command. On the other hand, when the comparison result shows “received SIR<target SIR”, the SIR calculator notifies the transmitter to transmit an “Up” command. A series of operation described above is referred to as an “inner-loop transmission power control.”
Secondly, “outer loop transmission power control” in the enhanced uplink will be described.
In step S201, a receiver of a radio network controller RNC measures a reception quality of the E-DPDCH (or of the DPDCH).
In step S202, a controller of the radio network controller RNC sets a target SIR in accordance with the measurement result, and notifies the target SIR to the radio base station Node B. In addition, the controller of the radio network controller RNC determines an amplitude ratio between the E-DPDCH and the DPCCH (hereinafter referred to as “gain factor”) in accordance with the measurement result so as to notify the determined amplitude ratio to the mobile station UE. Here, both of the E-DPDCH and the DPCCH are transmitted from the mobile station UE. A series of operation Is referred to as an “outer loop transmission power control.”
The outer loop transmission power control can be adapted to various fluctuation in the radio environment, such as when a mobile station UE shifts to a soft handover status, when a moving speed of the mobile station UE changes, when radio waves are interrupted by a building, or the like.
Further, since the outer loop transmission power control includes measuring the reception quality of the E-DPDCH as described above, the outer loop transmission power control is not performed when the transmission of the E-DPDCH does not exist.
Accordingly, for example, the following method has been proposed (for example, refer to Non-patent Document 1); The mobile station UE generates a transport block having a minimum transport block size, by inserting dummy data into such as MAC layer control information or blank information or the like (that is, performing a padding). Then, the mobile station UE transmits, at a predetermined transmission period, the transport block by using an Enhanced Dedicated Physical Control Channel (E-DPCCH) and the E-DPDCH.
According to the above-described method, even when data to be transmitted does not exist in the mobile station UE, the radio network controller RNC enables to measure the reception quality of the E-DPDCH, and thus the outer loop transmission power control can be performed. Therefore, it is possible to reduce deterioration in a radio quality caused by an interruption of transmission data.
However, in the above-described method, there has been a problem that, since the transmission timing of the transport block (that is, a frame number of the frame used for transmitting the transport block) is not previously notified to the RNC, the radio network controller RNC cannot detect the E-DPDCH when the E-DPCCH cannot be detected correctly. In that case, the outer loop transmission power control cannot be performed.
Non-patent Document 1: 3GPP TSG-RAN R2-05937